Difference b/w had to and would have to

“ Dinner at Billy's was more a punishment than a reward, since anyone who sat at the dinner table would have to listen to Billy's father's interminable harangues against the government.”

Could someone please clarify why the author has used “would have to” instead of “had to” in the above sentence? I’m not acquainted with this usage of would; what is it?

I think this looks like a conditional sentence:

If anyone sat at the dinner table they would have to listen to Billy's father's interminable harangues against the government.”

So I presume the author is not only referring to this particular occasion, especially because of the use of anyone. Whosoever sits at that table will have to listen to him. I hope this helps.